The physical layer of a wireless local area network supports a link adaptation technology (Link Adaptation). The main procedure of the link adaptation technology is as follows: after a transmitter sends data to a user by using a certain modulation and coding scheme (Modulation and Coding Scheme, MCS), due to the impact of channel conditions, and because a receiver can estimate actual channel state information, the receiver calculates parameters such as the parameters related to the channel conditions and the recommended MCS according to the channel conditions and transmission conditions (for example, the MCS) after receiving the data, and feeds back the parameters to the transmitter. After obtaining the parameters fed back by the receiver, the transmitter adjusts and selects a proper modulation and coding scheme to reduce the bit error rate of data transmission. The process of adjusting the MCS of the transmitter through modulation and coding scheme feedback (Modulation and Coding Scheme Feedback, MFB) of the receiver is a typical representative of the link adaptation technology.
The conventional wireless local area network system supports two feedback mechanisms: solicited feedback and unsolicited feedback. Solicited feedback means that after the transmitter sends a modulation and coding scheme request (MCS Request, MRQ) to the receiver, the receiver performs MFB with respect to the data of the previous frame sent by the transmitter; unsolicited feedback means that the receiver actively performs MFB, without requiring the transmitter to send a request. The unsolicited feedback may relate to the data of any one frame or multiple frames sent by the transmitter previously.
In the current new wireless local area network standard, a high throughput control field (High Throughput, HT, Control field) is introduced, and is used for link adaptation feedback, RDG (Reverse Direct Grant) indication, and so on. In the new standard, a similar control field is required to implement the functions. However, no new very high throughput control field (Very High Throughput, VHT, Control field) is defined at present, and the HT Control field is reused. Specifically, the first bit B0 that is originally a reserved bit in the HT Control field is used to differentiate two modes. When B0=0, it indicates that the current field is an HT Control field in the HT format (HT format HT Control field); when B0=1, it indicates that the current field is an HT Control field in the VHT format (VHT format HT Control field).
However, for the VHT format HT Control field, the reuse technology decreases the reserved bit, which is unfavorable for subsequently introducing newer technologies.